Intermediate thermal expansion coefficient glass

ABSTRACT

CTE-matched silicate glasses and more particularly to low-alkali CTE-matched silicate glasses that are useful in semiconductor-based applications, such as photovoltaics are described along with methods of making such glasses.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/890,638 filed on May 9, 2013, which is a Continuation-in-Part of U.S.application Ser. No. 12/573,213, which claims the benefit of priority toU.S. Prov. Appl. No. 61/103,126 filed on Oct. 6, 2008 and to U.S. Prov.Appl. No. 61/177,827 filed on May 13, 2009; Continuation-in-Part of U.S.application Ser. No. 13/305,051, which claims the benefit of priority toU.S. Prov. Appl. No. 61/418,084 filed on Nov. 30, 2010, U.S. Prov. Appl.No. 61/503,248 filed on Jun. 30, 2011, and U.S. Prov. Appl. No.61/562,651 filed on Nov. 22, 2011; Continuation-in-Part of U.S.application Ser. No. 13/569,756, which claims the benefit of priority toU.S. Prov. Appl. No. 61/522,956 filed on Aug. 12, 2011; andContinuation-in-Part of PCT/US12/49718 which claims benefit of priorityto U.S. Prov. Appl. No. 61/515,042 filed on Aug. 4, 2011 and U.S. Prov.Appl. No. 61/565,050 filed on Nov. 30, 2011, all of which are herebyincorporated by reference in their entirety.

BACKGROUND

Field

Embodiments relate generally to CTE-matched glasses and moreparticularly to low- to no-alkali aluminosilicate, borosilicate, andaluminoborosilicate glasses which may be useful in semiconductor-basedapplications, such as photovoltaics, photochromics, electrochromics, orOrganic Light Emitting Diode (OLED) applications.

Technical Background

The fusion forming process typically produces flat glass with optimalsurface and geometric characteristics useful for many electronicsapplications, for instance, substrates used in electronics applications,for example, display glass for LCD televisions.

Over the last 10 years, Corning fusion glass products include 1737F™,1737G™ Eagle2000F™, EagleXG™, Jade™, and Gorilla Glass™. Efficientmelting is generally believed to occur at a temperature corresponding toa melt viscosity of about 200 poise (P). These glasses share in common200 P temperatures in excess of 1600° C., which can translate toaccelerated tank and electrode corrosion, greater challenges for finingdue to still more elevated finer temperatures, and/or reduced platinumsystem life time, particularly around the finer. Many have temperaturesat 3000 P in excess of about 1300° C., and since this is a typicalviscosity for an optical stirrer, the high temperatures at thisviscosity can translate to excessive stirrer wear and elevated levels ofplatinum defects in the body of the glass.

Many of the above described glasses have delivery temperatures in excessof 1200° C., and this can contribute to creep of isopipe refractorymaterials, particularly for large sheet sizes.

These attributes combine so as to limit flow (because of slow meltrates), to accelerate asset deterioration, to force rebuilds ontimescales much shorter than product lifetimes, to force unacceptable(arsenic), expensive (capsule) or unwieldy (vacuum fining) solutions todefect elimination, and thus contribute in significant ways to the costof manufacturing glass.

In applications in which rather thick, comparatively low-cost glass withless extreme properties is required, these glasses are not onlyoverkill, but prohibitively expensive to manufacture. This isparticularly true when the competitive materials are made by the floatprocess, a very good process for producing low cost glass with ratherconventional properties. In applications that are cost sensitive, suchas large-area photovoltaic panels and OLED lighting, this costdifferential has been large enough to make the price point of LCD-typeglasses unacceptable.

Competing with the cost constraints for is the continuing drive to makenew technologies, like PV, competitive with existing power productionmethods, e.g., hydro, coal, nuclear, wind, etc., in the power generationindustry. To do so, in addition to cost, manufacturers are looking atconversion efficiency, device lifetime, and efficiencydegradation—design challenges that need to be addressed to make PV aviable alternative. Soda lime glass has been a common substrate for mostPV panels because of its low cost. However, soda lime glasses are notideal for PV modules, especially CdTe-based thin film PV modules assodium can cause problems with efficiency and device lifetime. Further,soda lime glasses can have sodium release issues that occur due toenvironmental conditions. These problems can lead to delamination issuesand reduced efficiency. Clearly, there is still an unmet need to findglass compositions that provide optimal substrates for thin film PVdevices.

SUMMARY

A first aspect comprises a glass comprising about, in mol %, 60 to 65percent SiO₂, 8 to 12 percent Al₂O₃, 7 to 15 percent B₂O₃, 0 to 8percent M₂O, and 9 to 15 percent RO, wherein, M is an alkali metal andwherein, R is an alkaline earth metal, and the glass has a coefficientof thermal expansion of from about 4.0 to about 7.5 ppm/° C. from 25 to300° C. In some embodiments, the glass has a coefficient of thermalexpansion of from about 4.5 to about 6.5 ppm/° C. from 25 to 300° C. Insome embodiments, the glass has a coefficient of thermal expansion offrom about 4.5 to about 6.0 ppm/° C. from 25 to 300° C. In someembodiments, the glass comprises about 0.1 to 8 mol % M₂O. In someembodiments, the glass further comprises about 0.01 to 0.4 percent SnO₂.

In some embodiments, the glass described above comprises about, in mol%, 61 to 64 percent SiO₂, 8 to 12 percent Al₂O₃, 9 to 15 percent B₂O₃,greater than 0 to 4 percent M₂O, and 12 to 15 percent RO.

In some embodiments, the glass described above comprises about, in mol%, 60 to 65 percent SiO₂, 8 to less than 10 percent Al₂O₃, greater than11 to 15 percent B₂O₃, greater than 0 to less than 1 percent M₂O, and 9to 15 percent RO.

In other embodiments, the glass described above comprises about, in mol%, 60 to 65 percent SiO₂, 10 to 12 percent Al₂O₃, 7 to 11 percent B₂O₃,1 to 8 percent M₂O, and 9 to 15 percent RO.

In other embodiments, the glass described above comprises about, in mol%, 62 to 65 percent SiO₂, 10 to 12 percent Al₂O₃, 7 to 11 percent B₂O₃,3 to 8 percent MgO, 3 to 10 percent CaO, 3 to 8 percent SrO, and 1 to 8percent M₂O, wherein, CaO/(CaO+SrO) is from 0.4 and 1.

A second aspect comprises a glass comprising about, in mol %, 20 to 70percent SiO₂, 5 to 20 percent Al₂O₃, 0 to 15 percent B₂O₃, 0 to 1percent M₂O, 0 to 10 percent MgO, 8 to 35 percent CaO, 0 to 16 percentSrO, 0 to 9 percent BaO, and 20 to 45 percent RO, wherein, M is analkali metal and wherein, R is an alkaline earth metal, and the glasshas a coefficient of thermal expansion of from about 4.0 to about 7.5ppm/° C. from 25 to 300° C. In some embodiments, the glass has acoefficient of thermal expansion of from about 4.5 to about 6.5 ppm/° C.from 25 to 300° C. In some embodiments, the glass has a coefficient ofthermal expansion of from about 4.5 to about 6.0 ppm/° C. from 25 to300° C. In some embodiments, the glass comprises about, in mol %, 57 to68 percent SiO₂, 5 to 12 percent Al₂O₃, 0 to 8 percent B₂O₃, 0 to 0.1percent M₂O, 0 to 10 percent MgO, 8 to 28 percent CaO, 0 to 10 percentSrO, 0 to 9 percent BaO, and 21 to 32 percent RO, wherein, M is analkali metal and wherein, R is an alkaline earth metal, and the glasshas a coefficient of thermal expansion of from about 4.0 to about 6.0ppm/° C. from 25 to 300° C.

A third aspect comprises a glass comprising about, in mol %, 60 to 68percent SiO₂, 8 to 11 percent Al₂O₃, 6 to 11 percent B₂O₃, 0 to 1percent M₂O; 0 to 5 percent MgO, greater than 0 to 12 percent CaO, 1 to12 percent SrO, 0 to 8 percent BaO, and 16 to 20 percent RO, wherein Ris an alkaline earth metal, and M is an alkali metal, and the glass hasa coefficient of thermal expansion of from about 4.0 to about 7.5 ppm/°C. from 25 to 300° C. In some embodiments, the glass has a coefficientof thermal expansion of from about 4.5 to about 6.5 ppm/° C. from 25 to300° C. In some embodiments, the glass has a coefficient of thermalexpansion of from about 4.5 to about 6.0 ppm/° C. from 25 to 300° C.

In some embodiments, the glasses described above are substantially freeof BaO, Sb₂O₃, As₂O₃, or combinations thereof. In some embodiments, theglasses described above further comprises 2 mole percent or less ofTiO₂, MnO, ZnO, Nb₂O₅, MoO₃, Ta₂O₅, WO₃, ZrO₂, Y₂O₃, La₂O₃, P₂O₅, orcombinations thereof. In some embodiments, the glass is ion exchanged.

A fourth aspect comprises a photovoltaic (“PV”) module, comprising aCdTe solar cell material, one or more conductive oxides, and a glasssubstrate, wherein the glass substrate has a coefficient of thermalexpansion of from about 4.0 to about 7.5 ppm/° C. from 25 to 300° C. Insome embodiments, the glass substrate has a coefficient of thermalexpansion of from about 4.5 to about 6.0 ppm/° C. from 25 to 300° C.

In some embodiments, the glass substrate in the PV module comprisesabout, in mol %, 60 to 65 percent SiO₂, 8 to 12 percent Al₂O₃, 7 to 15percent B₂O₃, 0 to 8 percent M₂O, and 9 to 15 percent RO, wherein, M isan alkali metal and wherein, R is an alkaline earth metal. In someembodiments, in the glass substrate in the PV module comprises, in mol%, 60 to 65 percent SiO₂, 8 to 12 percent Al₂O₃, 7 to 15 percent B₂O₃,0.1 to 8 percent M₂O, 9 to 15 percent RO, and 0.01 to 0.4 percent SnO₂.

In some embodiments, the glass substrate in the PV module comprisesabout, in mol %, 20 to 70 percent SiO₂, 5 to 20 percent Al₂O₃, 0 to 15percent B₂O₃, 0 to 1 percent M₂O, 0 to 10 percent MgO, 8 to 35 percentCaO, 0 to 16 percent SrO, 0 to 9 percent BaO, and 20 to 45 percent RO,wherein, M is an alkali metal and wherein, R is an alkaline earth metal.

In some embodiments, the glass substrate in the PV module comprisesabout, in mol %, 57 to 68 percent SiO₂, 5 to 12 percent Al₂O₃, 0 to 8percent B₂O₃, 0 to 0.1 percent M₂O, 0 to 10 percent MgO, 8 to 28 percentCaO, 0 to 10 percent SrO, 0 to 9 percent BaO, and 21 to 32 percent RO,wherein, M is an alkali metal and wherein, R is an alkaline earth metal,and the glass has a coefficient of thermal expansion of from about 4.0to about 6.0 ppm/° C. from 25 to 300° C.

In some embodiments, the glass substrate in the PV module comprisesabout, in mol %, 60 to 68 percent SiO₂, 8 to 11 percent Al₂O₃, 6 to 11percent B₂O₃, 0 to 1 percent M₂O; 0 to 5 percent MgO, greater than 0 to12 percent CaO, 1 to 12 percent SrO, 0 to 8 percent BaO, and 16 to 20percent RO, wherein R is an alkaline earth metal, and M is an alkalimetal.

A fifth aspect comprises a PV device, comprising a CdTe solar cellmaterial having a coefficient of thermal expansion, one or moreconductive oxides, and a glass substrate, wherein the glass substratehas a coefficient of thermal expansion that is within about ±2.0 ppm/°C. of the coefficient of thermal expansion of the CdTe solar cellmaterial from 25 to 300° C. In some embodiments, the glass substrate inthe PV module has a coefficient of thermal expansion of within about±1.0 ppm/° C. of the coefficient of thermal expansion of the CdTe solarcell material from 25 to 300° C.

In some embodiments, the glass substrate in the PV device comprisesabout, in mol %, 60 to 65 percent SiO₂, 8 to 12 percent Al₂O₃, 7 to 15percent B₂O₃, 0 to 8 percent M₂O, and 9 to 15 percent RO, wherein, M isan alkali metal and wherein, R is an alkaline earth metal. In someembodiments, in the glass substrate in the PV module comprises, in mol%, 60 to 65 percent SiO₂, 8 to 12 percent Al₂O₃, 7 to 15 percent B₂O₃,0.1 to 8 percent M₂O, 9 to 15 percent RO, and 0.01 to 0.4 percent SnO₂.

In some embodiments, the glass substrate in the PV device comprisesabout, in mol %, 20 to 70 percent SiO₂, 5 to 20 percent Al₂O₃, 0 to 15percent B₂O₃, 0 to 1 percent M₂O, 0 to 10 percent MgO, 8 to 35 percentCaO, 0 to 16 percent SrO, 0 to 9 percent BaO, and 20 to 45 percent RO,wherein, M is an alkali metal and wherein, R is an alkaline earth metal.

In some embodiments, the glass substrate in the PV device comprisesabout, in mol %, 57 to 68 percent SiO₂, 5 to 12 percent Al₂O₃, 0 to 8percent B₂O₃, 0 to 0.1 percent M₂O, 0 to 10 percent MgO, 8 to 28 percentCaO, 0 to 10 percent SrO, 0 to 9 percent BaO, and 21 to 32 percent RO,wherein, M is an alkali metal and wherein, R is an alkaline earth metal,and the glass has a coefficient of thermal expansion of from about 4.0to about 6.0 ppm/° C. from 25 to 300° C.

In some embodiments, the glass substrate in the PV device comprisesabout, in mol %, 60 to 68 percent SiO₂, 8 to 11 percent Al₂O₃, 6 to 11percent B₂O₃, 0 to 1 percent M₂O; 0 to 5 percent MgO, greater than 0 to12 percent CaO, 1 to 12 percent SrO, 0 to 8 percent BaO, and 16 to 20percent RO, wherein R is an alkaline earth metal, and M is an alkalimetal.

Additional features and advantages will be set forth in the detaileddescription which follows, and in part will be readily apparent to thoseskilled in the art from the description or recognized by practicing theinvention as described in the written description and claims hereof, aswell as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are merely exemplary of theinvention, and are intended to provide an overview or framework forunderstanding the nature and character of the invention as it isclaimed.

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate one or moreembodiment(s) of the invention and together with the description serveto explain the principles and operation of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be understood from the following detailed descriptioneither alone or together with the accompanying drawing figures.

FIG. 1 is a graph of estimated liquidus viscosity.

FIG. 2 is an illustration of features of a photovoltaic device accordingto one embodiment.

FIG. 3 shows the measured residual in-plane bulk stress of CdTe filmversus CTE of glass is represented with black markers and the blackdashed line is the linear fit. The corresponding device efficiency isrepresented by the blue marker. The shaded area represents the CTE rangeof a CdTe film. The dash black line shows the residual stress in theCdTe film trends towards a minimum as the glass CTE approaches the CTEof the CdTe film in the shaded area. The corresponding efficiency datapoints show the best performance for the device film with the lowestresidual stress magnitude. This suggests higher efficiencies can beobtained using a glass superstrate with a CTE that is matched to that ofthe CdTe film.

FIG. 4 is a graph of the CdTe film residual stress and correspondingefficiencies for devices fabricated using the close spaced sublimationprocess on glass substrates with varying CTE.

FIG. 5 is a graph of the efficiency and corresponding defect density asa function of the CdTe film residual stress for the same devices in FIG.4.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of theinvention. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like features.

In the following detailed description, numerous specific details may beset forth in order to provide a thorough understanding of embodiments ofthe invention. However, it will be clear to one skilled in the art whenembodiments of the invention may be practiced without some or all ofthese specific details. In other instances, well-known features orprocesses may not be described in detail so as not to unnecessarilyobscure the invention. In addition, like or identical reference numeralsmay be used to identify common or similar elements. Moreover, unlessotherwise defined, all technical and scientific terms used herein havethe same meaning as commonly understood by one of ordinary skill in theart to which this invention belongs. In case of conflict, the presentspecification, including the definitions herein, will control.

Although other methods and can be used in the practice or testing of theinvention, certain suitable methods and materials are described herein.

Disclosed are materials, compounds, compositions, and components thatcan be used for, can be used in conjunction with, can be used inpreparation for, or are embodiments of the disclosed method andcompositions. These and other materials are disclosed herein, and it isunderstood that when combinations, subsets, interactions, groups, etc.of these materials are disclosed that while specific reference of eachvarious individual and collective combinations and permutation of thesecompounds may not be explicitly disclosed, each is specificallycontemplated and described herein.

Thus, if a class of substituents A, B, and C are disclosed as well as aclass of substituents D, E, and F, and an example of a combinationembodiment, A-D is disclosed, then each is individually and collectivelycontemplated. Thus, in this example, each of the combinations A-E, A-F,B-D, B-E, B-F, C-D, C-E, and C-F are specifically contemplated andshould be considered disclosed from disclosure of A, B, and/or C; D, E,and/or F; and the example combination A-D. Likewise, any subset orcombination of these is also specifically contemplated and disclosed.Thus, for example, the sub-group of A-E, B-F, and C-E are specificallycontemplated and should be considered disclosed from disclosure of A, B,and/or C; D, E, and/or F; and the example combination A-D. This conceptapplies to all aspects of this disclosure including, but not limited toany components of the compositions and steps in methods of making andusing the disclosed compositions. Thus, if there are a variety ofadditional steps that can be performed it is understood that each ofthese additional steps can be performed with any specific embodiment orcombination of embodiments of the disclosed methods, and that each suchcombination is specifically contemplated and should be considereddisclosed.

Moreover, where a range of numerical values is recited herein,comprising upper and lower values, unless otherwise stated in specificcircumstances, the range is intended to include the endpoints thereof,and all integers and fractions within the range. It is not intended thatthe scope of the invention be limited to the specific values recitedwhen defining a range. Further, when an amount, concentration, or othervalue or parameter is given as a range, one or more preferred ranges ora list of upper preferable values and lower preferable values, this isto be understood as specifically disclosing all ranges formed from anypair of any upper range limit or preferred value and any lower rangelimit or preferred value, regardless of whether such pairs areseparately disclosed. Finally, when the term “about” is used indescribing a value or an end-point of a range, the disclosure should beunderstood to include the specific value or end-point referred to.

As used herein, the term “about” means that amounts, sizes,formulations, parameters, and other quantities and characteristics arenot and need not be exact, but may be approximate and/or larger orsmaller, as desired, reflecting tolerances, conversion factors, roundingoff, measurement error and the like, and other factors known to those ofskill in the art. In general, an amount, size, formulation, parameter orother quantity or characteristic is “about” or “approximate” whether ornot expressly stated to be such.

The term “or”, as used herein, is inclusive; more specifically, thephrase “A or B” means “A, B, or both A and B”. Exclusive “or” isdesignated herein by terms such as “either A or B” and “one of A or B”,for example.

The indefinite articles “a” and an are employed to describe elements andcomponents of the invention. The use of these articles means that one orat least one of these elements or components is present. Although thesearticles are conventionally employed to signify that the modified nounis a singular noun, as used herein the articles “a” and an also includethe plural, unless otherwise stated in specific instances. Similarly,the definite article “the”, as used herein, also signifies that themodified noun may be singular or plural, again unless otherwise statedin specific instances.

For the purposes of describing the embodiments, it is noted thatreference herein to a variable being a “function” of a parameter oranother variable is not intended to denote that the variable isexclusively a function of the listed parameter or variable. Rather,reference herein to a variable that is a “function” of a listedparameter is intended to be open ended such that the variable may be afunction of a single parameter or a plurality of parameters.

It is noted that terms like “preferably,” “commonly,” and “typically,”when utilized herein, are not utilized to limit the scope of the claimedinvention or to imply that certain features are critical, essential, oreven important to the structure or function of the claimed invention.Rather, these terms are merely intended to identify particular aspectsof an embodiment of the present disclosure or to emphasize alternativeor additional features that may or may not be utilized in a particularembodiment of the present disclosure.

For the purposes of describing and defining the claimed invention it isnoted that the terms “substantially” and “approximately” are utilizedherein to represent the inherent degree of uncertainty that may beattributed to any quantitative comparison, value, measurement, or otherrepresentation. The terms “substantially” and “approximately” are alsoutilized herein to represent the degree by which a quantitativerepresentation may vary from a stated reference without resulting in achange in the basic function of the subject matter at issue.

It is noted that one or more of the claims may utilize the term“wherein” as a transitional phrase. For the purposes of defining thepresent invention, it is noted that this term is introduced in theclaims as an open-ended transitional phrase that is used to introduce arecitation of a series of characteristics of the structure and should beinterpreted in like manner as the more commonly used open-ended preambleterm “comprising.”

As a result of the raw materials and/or equipment used to produce theglass composition of the present invention, certain impurities orcomponents that are not intentionally added, can be present in the finalglass composition. Such materials are present in the glass compositionin minor amounts and are referred to herein as “tramp materials.”

As used herein, a glass composition having 0 wt % of a compound isdefined as meaning that the compound, molecule, or element was notpurposefully added to the composition, but the composition may stillcomprise the compound, typically in tramp or trace amounts. Similarly,“sodium-free,” “alkali-free,” “potassium-free” or the like are definedto mean that the compound, molecule, or element was not purposefullyadded to the composition, but the composition may still comprise sodium,alkali, or potassium, but in approximately tramp or trace amounts.

It has been found that the CTE of the super/substrate glass for CdTethin-film photovoltaic modules should match, or be as closely matched aspossible, to the CTE of the semiconductor film so as to minimize thelevel of stress in said film and consequently optimize the efficiency ofthe photovoltaic module. The compositions described herein specifies aglass super/substrate having a CTE in the range that is optimum forminimizing the resultant stress in the semiconductor layers of CdTedevices and provide improved conversion efficiency in the resultingdevices.

The terms “solar cell,” “photovoltaic cell,” “PV cell,” “solar module,”“photovoltaic module,” “PV module,” “solar device,” “photovoltaicdevice,” “PV device,” or “device,” as used herein, refer to any articlethat can convert light into electrical energy. Suitable solar cellsinclude wafer-based solar cells (e.g., solar cells comprising materialsselected from crystalline-Si (c-Si), ribbon Si, or multi-crystalline-Si(mc-Si)(also called polycrystalline Si), and mixtures thereof). A solarcell assembly can comprise one or a plurality of solar cells. Theplurality of solar cells can be electrically interconnected or arrangedin a flat plane. In addition, the solar cell assembly can furthercomprise conductive pastes or electrical wirings deposited upon thesolar cells.

As used herein, the term “substrate” can be used to describe either asubstrate or a superstrate depending on the configuration of thephotovoltaic cell. For example, the substrate is a superstrate, if whenassembled into a photovoltaic cell, it is on the light incident side ofa photovoltaic cell. The superstrate can provide protection for thephotovoltaic materials from impact and environmental degradation whileallowing transmission of the appropriate wavelengths of the solarspectrum. Further, multiple photovoltaic cells can be arranged into aphotovoltaic module.

As used herein, the term “adjacent” can be defined as being in closeproximity. Adjacent structures may or may not be in physical contactwith each other. Adjacent structures can have other layers and/orstructures disposed between them.

As used herein, the term “planar” can be defined as having asubstantially topographically flat surface.

Although exemplary numerical ranges are described in the embodiments,each of the ranges can include any numerical value including decimalplaces within the range including each of the ranges endpoints.

As used herein, multivalent components of the exemplary compositions arerepresented, for example, as Fe₂O₃, SnO₂, As₂O₅, Sb₂O₅. These materialsare batched as said oxides but mixed valences or alternative valencescould be used.

In the broadest terms, the glass compositions described here have astrain point of 600° C. or greater and a CTE that is matched to a CdTethin film to be coated thereon. In some embodiments, “matched,” as usedherein, mean the CTE of the glass substrate is equivalent to within ±2,±1.5, ±1.0, ±0.75, ±0.5, or ±0.25 ppm/° C. of the CTE of a CdTe thinfilm to be coated thereon. In some embodiments, the CTE of the glasssubstrate is from about 4 ppm/° C. to about 8 ppm/° C., from about 4.5ppm/° C. to about 8 ppm/° C., from about 4.5 ppm/° C. to about 7 ppm/°C., from about 4.5 ppm/° C. to about 6.5 ppm/° C., from about 5 ppm/° C.to about 7 ppm/° C., from about 5.5 ppm/° C. to about 6.5 ppm/° C., fromabout 4 ppm/° C. to about 7 ppm/° C., from about 4 ppm/° C. to about 6.5ppm/° C., from about 5 ppm/° C. to about 8 ppm/° C., or from about 5.5ppm/° C. to about 8 ppm/° C. In some embodiments, the CTE of the glasssubstrate is about 4, 4.5, 5, 5.5, 5.75, 6.0, 6.5, 7, 7.5, or 8 ppm/° C.

Accordingly, in one embodiment, the glass has a strain point of 600° C.or greater, for example, 620° C. or greater. In some embodiments, theglass has a coefficient of thermal expansion of 38×10⁻⁷ or greater, forexample, 40×10⁻⁷ or greater, for example, 45×10⁻⁷ or greater.

The glass according to one embodiment can have a strain point of 620° C.or greater and/or a coefficient of thermal expansion of 45×10⁻⁷ orgreater.

In some embodiments, the CTE of the CdTe thin film comprises an averagevalue for a CdTe thin film. In some embodiments, the CTE of the CdTethin film comprises a specific CTE value for the CdTe film which resultsfrom the composition, substrate, other components, manufacturing ordeposition process.

A first aspect comprises a glass comprising, in mole percent, about:

-   -   20 to 70 percent SiO₂;    -   5 to 20 percent Al₂O₃;    -   0 to 15 percent B₂O₃;    -   0 to 1 percent M₂O;    -   0 to 10 percent MgO;    -   8 to 35 percent CaO;    -   0 to 16 percent SrO;    -   0 to 9 percent BaO; and    -   20 to 45 percent RO;        wherein, M is an alkali metal and wherein, R is an alkaline        earth metal.

In some embodiments, the glass comprises, in mole percent, about:

-   -   57 to 68 percent SiO₂;    -   5 to 12 percent Al₂O₃;    -   0 to 8 percent B₂O₃;    -   0 to 0.1 percent M₂O;    -   0 to 10 percent MgO;    -   8 to 28 percent CaO;    -   0 to 10 percent SrO;    -   0 to 9 percent BaO; and    -   21 to 32 percent RO;        wherein, M is an alkali metal and wherein, R is an alkaline        earth metal.

A second aspect comprises a glass comprising, in mole percent, about:

-   -   60 to 65 percent SiO₂;    -   8 to 12 percent Al₂O₃;    -   7 to 15 percent B₂O₃;    -   greater than 0 to 8 percent M₂O; and    -   9 to 15 percent RO;        wherein, M is an alkali metal and wherein, R is an alkaline        earth metal. According to another embodiment, the glass is        substantially free of BaO. For example, the content of BaO can        be 0.05 mole percent or less, for example, zero mole percent. In        another embodiment, the glass comprises 0.01 to 0.4 mole percent        SnO₂.

In some embodiment, the glass comprises, in mole percent, about:

-   -   61 to 64 percent SiO₂;    -   8 to 12 percent Al₂O₃;    -   9 to 15 percent B₂O₃;    -   greater than 0 to 4 percent M₂O; and    -   12 to 15 percent RO;        wherein, M is an alkali metal and wherein, R is an alkaline        earth metal.

In some embodiment, the glass comprises, in mole percent, about:

-   -   60 to 65 percent SiO₂;    -   8 to less than 10 percent Al₂O₃;    -   greater than 11 to 15 percent B₂O₃;    -   greater than 0 to less than 1 percent M₂O; and    -   9 to 15 percent RO;        wherein, M is an alkali metal and wherein, R is an alkaline        earth metal.

In some embodiment, the glass comprises, in mole percent, about:

-   -   60 to 65 percent SiO₂;    -   10 to 12 percent Al₂O₃;    -   7 to 11 percent B₂O₃;    -   1 to 8 percent M₂O; and    -   9 to 15 percent RO;        wherein, M is an alkali metal and wherein, R is an alkaline        earth metal.

In some embodiment, the glass comprises, in mole percent, about:

-   -   62 to 65 percent SiO₂;    -   10 to 12 percent Al₂O₃;    -   7 to 11 percent B₂O₃;    -   3 to 8 percent MgO;    -   3 to 10 percent CaO;    -   3 to 8 percent SrO; and    -   1 to 8 percent M₂O;        wherein, M is an alkali metal selected from K, Na, and        combinations thereof and wherein, CaO/(CaO+SrO) is from 0.4 to        1.

A third aspect comprises a glass comprising, in mole percent, about:

-   -   60 to 68 percent SiO₂;    -   8 to 11 percent Al₂O₃;    -   6 to 11 percent B₂O₃;    -   0 to 1 percent M₂O;    -   0 to 5 percent MgO;    -   greater than 0 to 12 percent CaO;    -   1 to 12 percent SrO;    -   0 to 8 percent BaO; and    -   16 to 20 percent RO;        wherein R is an alkaline earth metal, and M is an alkali metal.        In some embodiments, the M2O is from 0 to about 0.1 mole        percent.

In some embodiments, M is an alkali metal selected from Li, Na, K, Rb,Cs, and a combination thereof. In some embodiments, M is selected fromLi, K, Cs, and a combination thereof. In one embodiment, R is selectedfrom Mg, Ca, Sr, Ba, and a combination thereof. In some embodiments, Ris selected from Mg, Ca, Sr, and a combination thereof.

SiO₂, an oxide involved in the formation of glass, functions tostabilize the networking structure of glass. In some embodiments, theglass composition comprises from about 20 to about 70 mol % SiO₂. Insome embodiments, the glass composition comprises from about 57 to about68 mol % SiO₂. In some embodiments, the glass composition can comprisefrom about 60 to about 68 mol % SiO₂. In some embodiments, the glasscomposition can comprise from about 60 to about 65 mol % SiO₂. In someembodiments, the glass composition can comprise from about 61 to about64 mol % SiO₂. In some embodiments, the glass composition can comprisefrom about 62 to about 65 mol % SiO₂. In some embodiments, the glasscomposition can comprise from about 20 to about 70 mol %, about 20 toabout 68 mol %, about 20 to about 65 mol %, about 20 to about 64 mol %,about 20 to 60 mol %, about 20 to 50 mol %, about 20 to about 40 mol %,about 20 mol % to about 30 mol %, about 30 to about 70 mol %, about 30to about 68 mol %, about 30 to about 65 mol %, about 30 to about 64 mol%, about 30 to 60 mol %, about 30 to 50 mol %, about 30 to about 40 mol%, about 40 to about 70 mol %, about 40 to about 68 mol %, about 40 toabout 65 mol %, about 40 to about 64 mol %, about 40 to 60 mol %, about40 to 50 mol %, about 50 to about 70 mol %, about 50 to about 68 mol %,about 50 to about 65 mol %, about 50 to about 64 mol %, about 50 to 60mol %, about 60 to about 70 mol %, about 60 to about 68 mol %, about 60to about 65 mol %, about 60 to about 64 mol %, about 61 to about 70 mol%, about 61 to about 68 mol %, about 61 to about 65 mol %, or about 61to about 64 mol %. In some embodiments, the glass composition comprisesabout 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35,36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53,54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, or 70mol % SiO₂.

Al₂O₃ may provide for a) maintaining the lowest possible liquidustemperature, b) lowering the expansion coefficient, or c) enhancing thestrain point. In some embodiments, the glass composition can comprisefrom about 5 to about 20 mol % Al₂O₃. In some embodiments, the glasscomposition can comprise from 5 to about 12 mol % Al₂O₃. In someembodiments, the glass composition can comprise from about 8 to about 12mol % Al₂O₃. In some embodiments, the glass composition can comprisefrom about 8 to about 11 mol % Al₂O₃. In some embodiments, the glasscomposition can comprise from about 8 to about 10 mol % Al₂O₃. In someembodiments, the glass composition can comprise from about 10 to about12 mol % Al₂O₃. In some embodiments, the glass can comprise from about 5to about 20 mol %, about 5 to about 15 mol %, about 5 to about 12 mol %,about 5 to about 11 mol %, about 5 to about 10 mol %, about 8 to about20 mol %, about 8 to about 15 mol %, about 8 to about 15 mol %, about 8to about 12 mol %, about 8 to about 11 mol %, about 8 to about 10 mol %,about 10 to about 20 mol %, about 10 to about 15 mol %, about 10 toabout 12 mol %, about 10 to about 11 mol %, or about 15 to about 20 mol% Al₂O₃. In some embodiments, the glass composition can comprise about5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 mol %Al₂O₃.

B₂O₃ can be used as a flux to soften glasses, making them easier tomelt. B₂O₃ may also react with non-bridging oxygen atoms (NBOs),converting the NBOs to bridging oxygen atoms through the formation ofBO₄ tetrahedra, which increases the toughness of the glass by minimizingthe number of weak NBOs. B₂O₃ also lowers the hardness of the glasswhich, when coupled with the higher toughness, decreases thebrittleness, thereby resulting in a mechanically durable glass, whichcan be advantageous for substrates used in photovoltaic applications. Insome embodiments, the glass composition can comprise from 0 to about 15mol % B₂O₃. In some embodiments, the glass composition can comprise from0 to about 8 mol % B₂O₃. In some embodiments, the glass composition cancomprise from about 7 to about 15 mol % B₂O₃. In some embodiments, theglass composition can comprise from about 9 to about 15 mol % B₂O₃. Insome embodiments, the glass composition can comprise from about 11 toabout 15 mol % B₂O₃. In some embodiments, the glass composition cancomprise from about 7 to about 11 mol % B₂O₃. In some embodiments, theglass composition can comprise from about 6 to about 11 mol % B₂O₃. Asmentioned above, the glasses, according some embodiments, comprise 7 to15 mole percent, for example, 7 to 11 mole percent B₂O₃. In someembodiments, the glass composition can comprise from 0 to about 15 mol%, 0 to 12 mol %, 0 to 11 mol %, 0 to about 10 mol %, about 5 to about15 mol %, about 5 to about 12 mol %, about 5 to about 11 mol %, about 5to about 10 mol %, about 6 to about 15 mol %, about 6 to about 12 mol %,about 6 to about 11 mol %, about 6 to about 10 mol %, about 7 to about15 mol %, about 7 to about 12 mol %, about 7 to about 11 mol %, about 7to about 10 mol %, about 9 to about 15 mol %, about 9 to about 12 mol %,about 9 to about 11 mol %, about 9 to about 10 mol %, about 10 to about15 mol %, about 10 to about 12 mol %, about 10 to about 11 mol %, about11 to about 15 mol %, about 11 to about 12 mol %, or about 12 to about15 mol %, B₂O₃. In some embodiments, the glass composition can compriseabout 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 mol %B₂O₃.

Also as mentioned above, the glasses, according to some embodiments, 9to 45 mole percent RO wherein, R is an alkaline earth metal. Since MgO,CaO and BaO are effective in decreasing the viscosity of glass at ahigher temperature and enhancing the viscosity of glass at a lowertemperature, they may be used for the improvement of the meltingproperty and enhancement of the strain point. However, if excessiveamounts of both MgO and CaO are used, there is an increasing trendtoward phase separation and devitrification of the glass. As definedherein, RO comprises the mol % of MgO, CaO, SrO, and BaO. In someembodiments, the glass composition can comprise from 20 to about 45 mol% RO. In some embodiments, the glass composition can comprise from 21 toabout 32 mol % RO. In some embodiments, the glass composition cancomprise from 9 to about 15 mol % RO. In some embodiments, the glasscomposition can comprise from about 12 to about 15 mol % RO. In someembodiments, the glass composition can comprise from about 16 to about20 mol % RO. In some embodiments, the glass composition can comprisefrom about 9 to about 45 mol %, about 9 to about 40 mol %, about 9 toabout 35 mol %, about 9 to about 32 mol %, about 9 to about 30 mol %,about 9 to 25 mol %, about 9 to 20 mol %, about 9 to about 15 mol %,about 12 to about 45 mol %, about 12 to about 40 mol %, about 12 toabout 35 mol %, about 12 to about 32 mol %, about 12 to about 30 mol %,about 12 to about 25 mol %, about 12 to about 20 mol %, about 12 toabout 15 mol %, about 16 to about 45 mol %, about 16 to about 40 mol %,about 16 to about 35 mol %, about 16 to about 32 mol %, about 16 toabout 25 mol %, about 16 to about 20 mol %, about 20 to about 45 mol %,about 20 to about 40 mol %, about 20 to about 35 mol %, about 20 toabout 32 mol %, about 20 to about 30 mol %, about 20 to about 25 mol %,about 21 to about 45 mol %, about 21 to about 40 mol %, about 21 toabout 35 mol %, about 21 to about 32 mol %, about 21 to about 30 mol %,about 21 to about 25 mol %, about 25 to about 45 mol %, about 25 toabout 40 mol %, about 25 to about 35 mol %, about 25 to about 32 mol %,about 25 to about 30 mol %, about 30 to about 45 mol %, about 30 toabout 40 mol %, about 30 to about 35 mol %, about 30 to about 32 mol %,about 32 to about 45 mol %, about 32 to about 40 mol %, about 32 toabout 35 mol %, about 35 to about 45 mol %, about 35 to about 40 mol %,or about 40 to about 45 mol % RO. In some embodiments, the glasscomposition can comprise about 9, 10, 11, 12, 13, 14, 15, 16, 17, 18,19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36,37, 38, 39, 40, 41, 42, 43, 44, or 45 mol % RO.

In some embodiments, MgO can be added to the glass to reduce meltingtemperature, increase strain point, or adjust CTE when used incombination with other alkaline earth compounds (e.g., CaO, SrO, andBaO). It can disadvantageously lower CTE relative to other alkalineearths (e.g., CaO, SrO, BaO), and so other adjustments may be made tokeep the CTE within the desired range. Examples of suitable adjustmentsinclude increase SrO at the expense of CaO, increasing alkali oxideconcentration, and replacing a smaller alkali oxide (e.g., Na₂O) inwhole or in part with a larger alkali oxide (e.g., K₂O). In someembodiments, the glass can comprise about 0 to about 10 mol % MgO. Theglass can comprise, for example, 1 to 8 mole percent MgO. In someembodiments, the glass composition can comprise greater than 0 to about5 mol % MgO. In some embodiments, the glass composition can compriseabout 3 to about 8 mol % MgO. In some embodiments, the glass compositioncan comprise 0 to about 10 mol %, 0 to about 8 mol %, 0 to about 5 mol%, 0 to about 4 mol %, 0 to about 3 mol %, 0 to about 2 mol %, 0 toabout 1 mol %, about 3 to about 10 mol %, about 3 to about 8 mol %,about 3 to about 5 mol %, about 5 to about 10 mol %, about 5 to about 8wt, or about 7 to about 10 mol % MgO. In some embodiments, the glasscompositions can comprise about 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 mol% MgO.

In some embodiments, CaO can contribute to higher strain point, lowerdensity, and lower melting temperature. More generally, it can be acomponent of certain possible devitrification phases, particularlyanorthite (CaAl₂Si₂O₈), and this phase has complete solid solution withan analogous sodium phase, albite (NaAlSi₃O₈). High Na and Ca contentstaken alone can cause liquidus temperatures to be unacceptably high.However, CaO sources include limestone, an inexpensive material, so tothe extent that volume and low cost are factors, in some embodiments itis can be useful to make the CaO content as high as can be reasonablyachieved relative to other alkaline earth oxides. In some embodiments,the glass composition about from 0 to about 35 mol % CaO. In someembodiments, the glass composition about from 8 to about 35 mol % CaO.In some embodiments, the glass composition can comprise from 8 to about28 mol % CaO. In some embodiments, the glass composition can comprisefrom 0 to about 12 mol % CaO. In some embodiments, the glass compositioncan comprise from >0 to about 12 mol % CaO. In some embodiments, theglass composition can comprise from about 3 to about 10 mol % CaO. Insome embodiments, the glass composition can comprise from 0 to about 35mol %, 0 to about 30 mol %, 0 to about 28 mol %, 0 to 25 mol %, 0 to 20mol %, 0 to about 15 mol %, 0 to about 12 mol %, 0 to about 10 mol %, 0to about 5 mol %, about 3 to about 35 mol %, about 3 to about 30 mol %,about 3 to about 28 mol %, about 3 to about 25 mol %, about 3 to about20 mol %, about 3 to about 15 mol %, about 3 to about 12 mol %, about 3to about 10 mol %, about 8 to about 35 mol %, about 8 to about 30 mol %,about 8 to about 28 mol %, about 8 to about 25 mol %, about 8 to about20 mol %, about 8 to about 15 mol %, about 8 to about 12 mol %, about 8to about 10 mol %, about 10 to about 35 mol %, about 10 to about 30 mol%, about 10 to about 25 mol %, about 10 to about 20 mol %, about 10 toabout 15 mol %, about 10 to about 12 mol %, about 15 to about 35 mol %,about 15 to about 30 mol %, about 15 to about 28 mol %, about 15 toabout 25 mol %, about 15 to about 20 mol %, about 20 to about 35 mol %,about 20 to about 30 mol %, about 20 to about 28 mol %, about 20 toabout 28 mol %, about 25 to about 35 mol %, about 25 to about 30 mol %,about 25 to about 28 mol %, about 28 to about 35 mol %, about 28 toabout 30 mol %, about 28 to about 30 mol %, or about 30 to about 35 mol% CaO. In some embodiments, the glass composition can comprise about 0,1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20,21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, or 35 mol % CaO.

SrO can contribute to higher coefficient of thermal expansion, and therelative proportion of SrO and CaO can be manipulated to improveliquidus temperature, and thus liquidus viscosity. In some embodiments,the glass can comprise from 0 to about 16 mol % SrO. In someembodiments, the glass can comprise from 0 to about 10 mol % SrO. Insome embodiments, the glass can comprise from 1 to about 12 mol % SrO.In other embodiments, the glass can comprise greater than 0 to about 16mol % SrO. The glasses can comprise, in some embodiments, 0 to 5 molepercent SrO. In certain embodiments, the glass contains no deliberatelybatched SrO, though it may be present as a contaminant in other batchmaterials. In some embodiments, the glass composition can comprise from0 to about 16 mol %, 0 to about 15 mol %, 0 to about 12 mol %, 0 toabout 10 mol %, 0 to about 8 mol %, 0 to about 5 mol %, 0 to about 3 mol%, about 3 to about 16 mol %, about 3 to about 15 mol %, about 3 toabout 12 mol %, about 3 to about 10 mol %, about 3 to about 8 mol %,about 3 to about 5 mol %, about 5 to about 16 mol %, about 5 to about 15mol %, about 5 to about 12 mol %, about 5 to about 10 mol %, about 5 toabout 8 mol %, about 8 to about 16 mol %, about 8 to about 15 mol %,about 8 to about 12 mol %, about 8 to about 10 mol %, about 10 to about16 mol %, about 10 to about 15 mol %, about 10 to about 12 mol %, about12 to about 16 mol %, about 12 to about 15 mol %, or about 15 to about16 mol %, SrO. In some embodiments, the glass composition can compriseabout 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or 16 mol %SrO.

In some embodiments, the ratio CaO/(CaO+SrO) is advantageously keptbetween 0.4 and 1 to obtain a good balance between liquidus temperature(and hence liquidus viscosity) and melting temperature. For example,compositions with low alkali concentrations and high SrO concentrationshave comparatively high melting temperatures, and if SrO is too highthen liquidus temperatures may be elevated as well relative to glasseswith more alkali oxide and lower SrO. However, for fixed concentrationsof all other components, a local minimum in liquidus temperature isoften obtained for CaO/(CaO+SrO) ratios between 0.4 and 1.

The glasses, according to some embodiments, comprise BaO. In certainembodiments, the glasses comprise less than 0.1 mole percent of BaO. Insome embodiments, the glass composition can comprise from 0 to 10 mol %BaO. In some embodiments, the glass composition can comprise from 0 to 9mol % BaO. In some embodiments, the glass composition can comprise fromabout greater than 0 to about 10 mol % BaO. In some embodiments, theglass composition can comprise from >0 to 8 mol % BaO. In someembodiments, the glass composition can comprise 0 to about 10 mol %, 0to about 9 mol %, 0 to about 8 mol %, 0 to about 5 mol %, 0 to about 3mol %, about 3 to about 10 mol %, about 3 to about 9 mol %, about 3 toabout 8 mol %, about 3 to about 5 mol %, about 5 to about 10 mol %,about 5 to about 9 mol %, about 5 to about 8 mol %, about 8 to about 9mol %, about 8 to about 10 mol %, or about 9 to about 10 mol % BaO. Insome embodiments, the glass composition comprises about 0, 1, 2, 3, 4,5, 6, 7, 8, 9, or 10 mol % BaO

Generally, alkali cations can raise the CTE steeply, but also can lowerthe strain point and, depending upon how they are added, they canincrease melting temperatures. The least effective alkali oxide forraising CTE is Li₂O, and the most effective alkali oxide for raising CTEis Cs₂O. In some embodiments, the glass composition can comprise from 0to about 8 mol % M₂O, wherein M is one or more of the alkali cations Na,Li, K, Rb, and Cs. In some embodiments, the glass composition cancomprise from greater than 0 to about 8 mol % M₂O. In some embodiments,the glass composition can comprise from greater than 0 to about 4 mol %M₂O. In some embodiments, the glass composition can comprise fromgreater than 0 to about 1 mol % M₂O. In some embodiments, M₂O cancomprise only trace amounts of Na₂O. In some embodiments, M₂O cancomprise only trace amounts of Na₂O and K₂O. In certain embodiments, thealkalis in question can be Li, K and Cs or combinations thereof. In someembodiments, the glass composition is substantially alkali free, forexample, the content of alkali metal can be about 1 weight percent orless, 0.5 weight percent or less, 0.25 mol % or less, 0.1 mol % or lessor 0.05 mol % or less. In some embodiments, M₂O is essentially 0 mol %or is only present in tramp amounts. The glass, according to someembodiments, can be substantially free of intentionally added alkalications, compounds, or metals. In some embodiments, the glasscomposition can comprises from 0 to about 8 mol %, 0 to about 7 mol %, 0to about 6 mol %, 0 to about 5 mol %, 0 to about 4 mol %, 0 to about 3mol %, 0 to about 2 mol %, 0 to about 1 mol %, >0 to about 8 mol %, >0to about 7 mol %, >0 to about 6 mol %, >0 to about 5 mol %, >0 to about4 mol %, >0 to about 3 mol %, >0 to about 2 mol %, >0 to about 1 mol %,about 1 to about 8 mol %, about 1 to about 7 mol %, about 1 to about 6mol %, about 1 to about 5 mol %, about 1 to about 4 mol %, about 1 toabout 3 mol %, about 1 to about 2 mol %, about 2 to about 8 mol %, about2 to about 7 mol %, about 2 to about 6 mol %, about 2 to about 5 mol %,about 2 to about 4 mol %, about 2 to about 3 mol %, about 3 to about 8mol %, about 3 to about 7 mol %, about 3 to about 6 mol %, about 3 toabout 5 mol %, about 3 to about 4 mol %, about 4 to about 8 mol %, about4 to about 7 mol %, about 4 to about 6 mol %, about 4 to about 5 mol %,about 5 to about 8 mol %, about 5 to about 7 mol %, about 5 to about 6mol %, about 6 to about 8 mol %, about 6 to about 7 mol %, or about 7 toabout 8 mol % M₂O. In some embodiments, the glass compositions cancomprise about 0, 1, 2, 3, 4, 5, 6, 7, or 8 mol % M₂O.

Sodium can be a mobile element or ion commonly used in standard windowsoda-lime glass compositions. The mobility of sodium can be problematicfor the long-term reliability of PV modules since over the life of a PVmodule sodium can drift out of the glass under an applied field andmigrate onto the active device layers of the module and degradeperformance over time. In some embodiments, the glass is substantiallysodium free. In some embodiments, the glass comprises 0.5 weight percentor less, 0.25 mol % or less, 0.1 mol % or less, about 0.05 mol % orless, or 0.001 mol % or less.

In alternative embodiments, sodium can be present from 0 to about 8 mol%. In some embodiments, the glass composition can comprises from 0 toabout 8 mol %, 0 to about 7 mol %, 0 to about 6 mol %, 0 to about 5 mol%, 0 to about 4 mol %, 0 to about 3 mol %, 0 to about 2 mol %, 0 toabout 1 mol %, >0 to about 8 mol %, >0 to about 7 mol %, >0 to about 6mol %, >0 to about 5 mol %, >0 to about 4 mol %, >0 to about 3 mol %, >0to about 2 mol %, >0 to about 1 mol %, about 1 to about 8 mol %, about 1to about 7 mol %, about 1 to about 6 mol %, about 1 to about 5 mol %,about 1 to about 4 mol %, about 1 to about 3 mol %, about 1 to about 2mol %, about 2 to about 8 mol %, about 2 to about 7 mol %, about 2 toabout 6 mol %, about 2 to about 5 mol %, about 2 to about 4 mol %, about2 to about 3 mol %, about 3 to about 8 mol %, about 3 to about 7 mol %,about 3 to about 6 mol %, about 3 to about 5 mol %, about 3 to about 4mol %, about 4 to about 8 mol %, about 4 to about 7 mol %, about 4 toabout 6 mol %, about 4 to about 5 mol %, about 5 to about 8 mol %, about5 to about 7 mol %, about 5 to about 6 mol %, about 6 to about 8 mol %,about 6 to about 7 mol %, or about 7 to about 8 mol % Na₂O. In someembodiments, the glass compositions can comprise about 0, 1, 2, 3, 4, 5,6, 7, or 8 mol % Na₂O.

As in the case of sodium, potassium is also an element or ion commonlyfound in standard window soda-lime glass compositions that hassubstantial mobility and may drift out of the glass. In someembodiments, the glass is substantially potassium free. In someembodiments, the glass comprises 0.5 weight percent or less, 0.25 mol %or less, 0.1 mol % or less, about 0.05 mol % or less, or 0.001 mol % orless.

In alternative embodiments, potassium can be present from 0 to about 8mol %. In some embodiments, the glass can comprises from 0 to about 8mol %, 0 to about 7 mol %, 0 to about 6 mol %, 0 to about 5 mol %, 0 toabout 4 mol %, 0 to about 3 mol %, 0 to about 2 mol %, 0 to about 1 mol%, >0 to about 8 mol %, >0 to about 7 mol %, >0 to about 6 mol %, >0 toabout 5 mol %, >0 to about 4 mol %, >0 to about 3 mol %, >0 to about 2mol %, >0 to about 1 mol %, about 1 to about 8 mol %, about 1 to about 7mol %, about 1 to about 6 mol %, about 1 to about 5 mol %, about 1 toabout 4 mol %, about 1 to about 3 mol %, about 1 to about 2 mol %, about2 to about 8 mol %, about 2 to about 7 mol %, about 2 to about 6 mol %,about 2 to about 5 mol %, about 2 to about 4 mol %, about 2 to about 3mol %, about 3 to about 8 mol %, about 3 to about 7 mol %, about 3 toabout 6 mol %, about 3 to about 5 mol %, about 3 to about 4 mol %, about4 to about 8 mol %, about 4 to about 7 mol %, about 4 to about 6 mol %,about 4 to about 5 mol %, about 5 to about 8 mol %, about 5 to about 7mol %, about 5 to about 6 mol %, about 6 to about 8 mol %, about 6 toabout 7 mol %, or about 7 to about 8 mol % K₂O. In some embodiments, theglass compositions can comprise about 0, 1, 2, 3, 4, 5, 6, 7, or 8 mol %K₂O

In certain embodiments, the glass satisfies one or more of the followingexpressions:1.0≤(M₂O+RO)/Al₂O₃≤2; and0.4≤CaO/(CaO+SrO)≤1.The ratio (M₂O+RO)/Al₂O₃ is advantageously greater than 1.0 to assist inremoving bubbles from the glass during the initial melt step. Thisoccurs because the alkali and alkaline earth metal oxides that are notinvolved in stabilizing Al₂O₃ are available to digest the silica source,typically a commercial sand. Surface area that might be sites for bubblenucleation and growth are therefore eliminated early in melting, and acomparatively bubble-free glass is obtained.

The glasses, according to some embodiments, can further comprise avariety of other components. For example, the glasses can comprise SnO₂,Fe₂O₃, MnO, CeO₂, As₂O₃, Sb₂O₃, Cl, Br, or combinations thereof. Thesematerials can be added as fining agents (e.g., to facilitate removal ofgaseous inclusions from melted batch materials used to produce theglass) and/or for other purposes. In certain embodiments, the glassescomprise SnO₂ (e.g., as calculated in mole percent on an oxide basis,0.02 to 0.3 SnO₂, etc.) and Fe₂O₃ (e.g., as calculated in mole percenton an oxide basis, 0.005 to 0.08 Fe₂O₃, 0.01 to 0.08 Fe₂O₃, etc.). Byway of illustration, in certain embodiments, the glasses comprise SnO₂and Fe₂O₃, wherein, in mole percent on an oxide basis:0.02≤SnO₂≤0.3; and0.005≤Fe₂O₃≤0.08.

In certain embodiments, the glasses comprise less than 0.05% molepercent of Sb₂O₃, As₂O₃, or combinations thereof. In certainembodiments, the glasses comprise SnO₂, Fe₂O₃, CeO₂, Cl, Br, orcombinations thereof and include less than 0.05% (e.g., less than 0.04%,less than 0.03%, less than 0.02%, less than 0.01%, etc.) mole percent ofSb₂O₃, As₂O₃, or combinations thereof. In certain embodiments, theglasses comprise SnO₂ and Fe₂O₃ and include less than 0.05 mole percent(e.g., less than 0.04 mole percent, less than 0.03 mole percent, lessthan 0.02 mole percent, less than 0.01 mole percent, etc.) of Sb₂O₃,As₂O₃, or combinations thereof. In certain embodiments, the glassescomprise SnO₂ and Fe₂O₃, wherein, in mole percent on an oxide basis:0.02≤SnO₂≤0.3; and0.005≤Fe₂O₃≤0.08,and include less than 0.05% mole percent of Sb₂O₃, As₂O₃, orcombinations thereof.

The glasses, according to some embodiments, (e.g., any of the glassesdiscussed above) can include F, Cl, or Br, for example, as in the casewhere the glasses comprise Cl and/or Br as fining agents. For example,the glass can comprise fluorine, chlorine, and/or bromine, wherein, ascalculated in mole percent: F+Cl+Br≤0.4, such as where F+Cl+Br≤0.3,F+Cl+Br≤0.2, F+Cl+Br≤0.1, 0.001≤F+Cl+Br≤0.4, and/or 0.005≤F+Cl+Br≤0.4.By way of illustration, in certain embodiments, the glass comprises SnO₂and Fe₂O₃ and, optionally, fluorine, chlorine, and/or bromine, suchthat, as calculated in mole percent on an oxide basis: 0.02≤SnO₂≤0.3,0.005≤Fe₂O₃≤0.08, and F+Cl+Br≤0.4; and, in certain embodiments, theglass comprises SnO₂ and Fe₂O₃ and, optionally, Sb₂O₃, As₂O₃, fluorine,chlorine, and/or bromine, such that, as calculated in mole percent on anoxide basis, 0.02≤SnO₂≤0.3, 0.005≤Fe₂O₃≤0.08, and F+Cl+Br≤0.4, and suchthat the glass includes less than 0.05 mole percent (e.g., less than0.04, less than 0.03, less than 0.02, less than 0.01, etc.) mole percentof Sb₂O₃, As₂O₃, or combinations thereof.

In some embodiments, the glass is substantially free of Sb₂O₃, As₂O₃, orcombinations thereof, for example, the glass comprises 0.05 mole percentor less of Sb₂O₃ or As₂O₃ or a combination thereof. For example, theglass can comprise zero mole percent of Sb₂O₃ or As₂O₃ or a combinationthereof.

The glass can further comprise 2 mole percent or less of TiO₂, MnO, ZnO,Nb₂O₅, MoO₃, Ta₂O₅, WO₃, ZrO₂, Y₂O₃, La₂O₃, HfO₂, CdO, SnO₂, Fe₂O₃,CeO₂, As₂O₃, Sb₂O₃, Cl, Br, P₂O₅, or combinations thereof.

The glasses, according to some embodiments, can further includecontaminants as typically found in commercially prepared glass. Inaddition or alternatively, a variety of other oxides (e.g., TiO₂, MnO,ZnO, Nb₂O₅, MoO₃, Ta₂O₅, WO₃, ZrO₂, Y₂O₃, La₂O₃, P₂O₅, and the like) canbe added, albeit with adjustments to other glass components, withoutcompromising their melting or forming characteristics. In those caseswhere the glasses, according to some embodiments, further include suchother oxide(s), each of such other oxides are typically present in anamount not exceeding 2 mole percent, and their total combinedconcentration is typically less than or equal to 5 mole percent,although higher amounts can be used so long as the amounts used do notplace the composition outside of the ranges described above. Theglasses, according to some embodiments, can also include variouscontaminants associated with batch materials and/or introduced into theglass by the melting, fining, and/or forming equipment used to producethe glass (e.g., ZrO₂).

The glass, according to some embodiments, is down-drawable; that is, theglass is capable of being formed into sheets using down-draw methodssuch as, but not limited to, fusion draw and slot draw methods that areknown to those skilled in the glass fabrication arts. Such down-drawprocesses are used in the large-scale manufacture of flat glass, forexample, display glass or ion-exchangeable glass.

The fusion draw process uses an isopipe that has a channel for acceptingmolten glass raw material. The channel has weirs that are open at thetop along the length of the channel on both sides of the channel. Whenthe channel fills with molten material, the molten glass overflows theweirs. Due to gravity, the molten glass flows down the outside surfacesof the isopipe. These outside surfaces extend down and inwardly so thatthey join at an edge below the drawing tank. The two flowing glasssurfaces join at this edge to fuse and form a single flowing sheet. Thefusion draw method offers the advantage that, since the two glass filmsflowing over the channel fuse together, neither outside surface of theresulting glass sheet comes in contact with any part of the apparatus.Thus, the surface properties are not affected by such contact.

The slot draw method is distinct from the fusion draw method. Here themolten raw material glass is provided to a conduit. The bottom of theconduit has an open slot that is wider in one dimension than the otherdimension with a nozzle that extends the length of the slot. The moltenglass flows through the slot/nozzle and is drawn downward as acontinuous sheet there through and into an annealing region. Compared tothe fusion draw process, the slot draw process provides a thinner sheet,as only a single sheet is drawn through the slot, rather than two sheetsbeing fused together, as in the fusion down-draw process.

In order to be compatible with down-draw processes, thealuminoborosilicate glass described herein has a high liquidusviscosity. In one embodiment, the glass has a liquidus viscosity of50,000 poise or greater, for example, 150,000 poise or greater, forexample, greater than or equal to 500,000 poise. The liquidusviscosities of the glasses are very closely correlated with thedifference between the liquidus temperature and the softening point.This correlation is indicated by line 10 in FIG. 1. For down drawprocesses, the glasses preferably have liquidus—softening point lessthan about 230° C., more preferably less than 200° C.

Alternatively, the glass, may be formed by other processes, such asrolling, float, etc.

According to one embodiment, the glass is ion exchanged in a salt bathcomprising one or more salts of alkali ions. The glass can be ionexchanged to change its mechanical properties. For example, smalleralkali ions, such as lithium or sodium, can be ion-exchanged in a moltensalt containing one or more larger alkali ions, such as sodium,potassium, rubidium or cesium. If performed at a temperature well belowthe strain point for sufficient time, a diffusion profile will form inwhich the larger alkali moves into the glass surface from the salt bath,and the smaller ion is moved from the interior of the glass into thesalt bath. When the sample is removed, the surface will go undercompression, producing enhanced toughness against damage. Such toughnessmay be desirable in instances where the glass will be exposed to adverseenvironmental conditions, such as photovoltaic grids exposed to hail. Alarge alkali already in the glass can also be exchanged for a smalleralkali in a salt bath. If this is performed at temperatures close to thestrain point, and if the glass is removed and its surface rapidlyreheated to high temperature and rapidly cooled, the surface of theglass will show considerable compressive stress introduced by thermaltempering. This will also provide protection against adverseenvironmental conditions. It will be clear to one skilled in the artthat any monovalent cation can be exchanged for alkalis already in theglass, including copper, silver, thallium, etc., and these also provideattributes of potential value to end uses, such as introducing color forlighting or a layer of elevated refractive index for light trapping.

In one embodiment, the glass is in the form of a sheet. The glass in theform of a sheet can be thermally tempered.

Another aspect comprises a photovoltaic thin-film solar devicecomprising the glass compositions described above as the startingsuper/substrate. In the case of CdTe-based modules, the design typicallycomprises the glass substrate, a transparent conductive oxide (“TCO”)such at fluorine doped tin oxide (“FTO”) or cadmium stannate (“CTO”),followed by resistive transparent layer such as tin oxide (“SnO₂”) orzinc doped tin oxide (“ZTO”). Next to the resistive transparent layer isa n-type semiconductor such as CdS followed by a p-type semiconductor,such as CdTe.

In one embodiment, a photovoltaic device comprises the glass in the formof a sheet. The photovoltaic device can comprise more than one of theglass sheets, for example, as a substrate and/or as a superstrate. Inone embodiment, the glass sheet is substantially planar. According toone embodiment, the glass sheet is transparent.

According to some embodiments, the glass sheet has a thickness of 4.0 mmor less, for example, 3.5 mm or less, for example, 3.2 mm or less, forexample, 3.0 mm or less, for example, 2.5 mm or less, for example, 2.0mm or less, for example, 1.9 mm or less, for example, 1.8 mm or less,for example, 1.5 mm or less, for example, 1.1 mm or less, for example,0.5 mm to 2.0 mm, for example, 0.5 mm to 1.1 mm, for example, 0.7 mm to1.1 mm. Although these are exemplary thicknesses, the glass sheet canhave a thickness of any numerical value including decimal places in therange of from 0.1 mm up to and including 4.0 mm.

In another embodiment, the photovoltaic device comprising a glass sheetand an active photovoltaic medium adjacent to the glass sheet.

In one embodiment, the active photovoltaic medium comprises cadmiumtelluride.

Another embodiment, as shown in FIG. 2 features 200 of a photovoltaicdevice comprising a glass sheet 12 comprising any of the glasscompositions previously described and an active photovoltaic medium 16adjacent to the glass sheet, wherein the active photovoltaic mediumcomprises cadmium telluride. According to one embodiment, the glasssheet has a thickness as previously described. The photovoltaic devicecan further comprise a conductive layer 14, such as a transparentconductive oxide adjacent to or disposed on the glass sheet.

EXAMPLES Example 1

The following is an example of how to fabricate a sample of an exemplaryglass, according to one embodiment of the invention, as shown inTable 1. This composition corresponds to composition number 46 shown inTable 7.

TABLE 1 Oxide mol % SiO₂ 63.5 Al₂O₃ 10.7 B₂O₃ 10.3 K₂O 2.3 MgO 4.4 CaO5.2 SrO 3.5 SnO₂ 0.1In some embodiments, the total does not add up to 100%, since certaintramp elements are present at non-negligible concentrations.

Batch materials, as shown in Table 2 were weighed and added to a 4 literplastic container:

TABLE 2 Batch Batch Components weight sand 1713.42 alumina 486.27 boricacid 570.42 Potassium carbonate 143.05 Magnesia 78.62 Limestone 240.73Strontium carbonate 234.23 10% SnO₂ and 90% sand 6.92

It should be appreciated that in the batch, limestone, depending on thesource can contain tramp elements and/or vary amounts of one or moreoxides, for example, MgO and/or BaO. The sand is advantageouslybeneficiated so that at least 80% by mass passes 60 mesh, for example 80mesh, for example 100 mesh. The SnO₂ added, in this example, waspre-mixed with sand at a level of 10% by weight so as to ensurehomogeneous mixing with the other components. The bottle containing thebatch materials was mounted to a tumbler and the batch materials weremixed so as to make a homogeneous batch and to break up softagglomerates. The mixed batch was transferred to a 1800 cc platinumcrucible and placed into a high-temperature ceramic backer. The platinumin its backer was loaded into a glo-bar furnace idling at a temperatureof 1550° C. After 6 hours, the crucible+backer was removed and the glassmelt was poured onto a cold surface, such as a steel plate, to form apatty, and then transferred to an annealer held at a temperature of 670°C. The glass patty was held at the annealer temperature for 2 hours,then cooled at a rate of 1° C. per minute to room temperature.

Tables 3-13 show exemplary glasses, according to embodiments of theinvention, and made according to the above example. Properties data forsome glasses are also shown in Tables 3-13.

In view of its low liquidus temperature of 940° C. and, hence, itsextremely high liquidus viscosity in excess of 5,000,000 poise, glass49, shown in Table 8 is an advantageous glass for applications, such asglass for photovoltaics. The exemplary glasses shown in Table 8comprise, in mole percent:

-   -   62 to 64 percent SiO₂;    -   8 to 12 percent Al₂O₃;    -   9 to 15 percent B₂O₃;    -   greater than 0 to 4 percent M₂O; and    -   12 to 15 percent RO;        wherein, M is an alkali metal and wherein, R is an alkaline        earth metal.

Further, the glasses shown in Table 8 have anneal points≥640° C.,thermal expansion coefficients (CTE) of 40-50×10⁻⁷/° C., 200 poisetemperatures of ≤1550° C., and liquidus viscosities of ≥500,000 poise.Liquidus viscosity may be dependent on the K₂O content, for example,exemplary glass 49 has a maximum value in excess of 5,000,000 poise foran intermediate K₂O content when compared to exemplary glasses 48, 50,and 51.

TABLE 3 Glass 1 2 3 4 5 Weight Percent SiO₂ 58.11 59.14 59.01 58.8858.35 Al₂O₃ 17.76 18.07 18.03 17.99 17.82 B₂O₃ 9.79 9.96 9.94 9.92 9.82MgO 3.26 4.45 3.88 3.31 3.27 CaO 4.03 4.10 4.87 5.64 4.04 SrO 2.85 0 0 00 BaO 0 0 0 0 0 Na₂O 3.98 4.05 4.04 4.03 3.99 K₂O 0 0 0 0 2.60 SnO₂ 0.230.23 0.23 0.23 0.12 Fe₂O₃ 0 0 0 0 0 total 100.01 100 100 100 100.01 MolePercent SiO₂ 63.3 63.3 63.3 63.3 63.35 Al₂O₃ 11.4 11.4 11.4 11.4 11.4B₂O₃ 9.2 9.2 9.2 9.2 9.2 MgO 5.3 7.1 6.2 5.3 5.3 CaO 4.7 4.7 5.6 6.5 4.7SrO 1.8 0 0 0 0 BaO 0 0 0 0 0 Na₂O 4.2 4.2 4.2 4.2 4.2 K₂O 0 0 0 0 1.8SnO₂ 0.1 0.1 0.1 0.1 0.05 Fe₂O₃ 0 0 0 0 0 total 100 100 100 100 100Properties strain 593 598 606 597 588 anneal 642 647 656 646 638softening point 867 868 882 874 881 CTE 44.9 44 43.5 46.4 50.1 density2.447 2.332 2.414 2.422 2.393 Viscosity A −2.2233 −2.5584 B 5556.586588.87 To 305.47 220.27 T @ 200 p 1533.625 1576.164 T @ 35 kP 1126.5541147.957 T @ 250 kP 1034.561 1048.398 T(200 P) − T(35 kP) 407.071428.206 Resistivity A 3.0838 3.9616 B 1183.49 4266.54 To 2156.83 3061.95R @ 200 p 15.30245 12.30353 Liquidus air 1070 1090 1065 1060 995internal 1060 1080 1060 1050 980 Pt 1040 1050 1030 1040 975 phase AlbiteAlbite Albite Albite Albite Liquidus viscosity 173742.1 1300909 Intliq - soft 193 212 178 176 99 estimated 107951.5 64408.99 168454.9179256.1 4244242 liquidus viscosity Glass 6 7 8 9 Weight Percent SiO₂58.40 58.54 58.74 58.56 Al₂O₃ 17.83 17.88 17.94 17.88 B₂O₃ 9.83 9.859.88 9.85 MgO 3.28 3.91 4.54 3.62 CaO 4.90 4.05 4.07 4.46 SrO 0 0 0 0BaO 0 0 0 0 Na₂O 3.04 3.05 2.10 3.34 K₂O 2.60 2.61 2.62 2.17 SnO₂ 0.120.12 0.12 0.12 Fe₂O₃ 0 0 0 0 total 100 100.01 100.01 100 Mole PercentSiO₂ 63.35 63.35 63.35 63.35 Al₂O₃ 11.4 11.4 11.4 11.4 B₂O₃ 9.2 9.2 9.29.2 MgO 5.3 6.3 7.3 5.83 CaO 5.7 4.7 4.7 5.17 SrO 0 0 0 0 BaO 0 0 0 0Na₂O 3.2 3.2 2.2 3.5 K₂O 1.8 1.8 1.8 1.5 SnO₂ 0.05 0.05 0.05 0.05 Fe₂O₃0 0 0 0 total 100 100 100 100 Properties strain 592 601 613 594 anneal643 652 663 646 softening point 885 890 901 883 CTE 47.8 47 43.7 47.2density 2.402 2.401 2.399 2.401 Viscosity A B To T @ 200 p T @ 35 kP T @250 kP T(200 P) − T(35 kP) Resistivity A B To R @ 200 p Liquidus air1050 1040 1115 1030 internal 1040 1030 1105 1020 Pt 1020 1015 1075 1000phase Albite Albite Albite Albite Liquidus viscosity Int liq - soft 155140 204 137 estimated 360553.2 631087.4 79584.37 710936.1 liquidusviscosity

TABLE 4 Glass 10 11 12 13 14 Weight Percent SiO₂ 58.78 57.16 57.49 57.8358.17 Al₂O₃ 17.95 17.46 17.56 17.66 17.76 B₂O₃ 9.89 9.62 9.67 9.73 9.79MgO 3.96 3.21 3.48 3.76 4.04 CaO 4.88 3.96 4.34 4.72 5.11 SrO 0 0 0 0 0BaO 0 0 0 0 0 Na₂O 2.68 0 0 0 0 K₂O 1.75 8.49 7.34 6.18 5.01 SnO₂ 0.120.11 0.11 0.11 0.12 Fe₂O₃ 0 0 0 0 0 total 100.01 100.01 99.99 99.99 100Mole Percent SiO₂ 63.35 63.35 63.35 63.35 63.35 Al₂O₃ 11.40 11.40 11.4011.40 11.40 B₂O₃ 9.20 9.20 9.20 9.20 9.20 MgO 6.36 5.30 5.72 6.14 6.56CaO 5.64 4.70 5.12 5.54 5.96 SrO 0 0 0 0 0 BaO 0 0 0 0 0 Na₂O 2.80 0 0 00 K₂O 1.20 6.00 5.16 4.32 3.48 SnO₂ 0.05 0.05 0.05 0.05 0.05 Fe₂O₃ 0 0 00 0 total 100 100 100 100 100 Properties strain 604 608 621 624 632anneal 655 661 674 675 685 softening point 885 914 911 916 925 CTE 44.552.1 48.9 45.6 44.1 density 2.411 2.382 2.389 2.393 2.397 Viscosity A−2.7798 −2.7896 B 6788.52 6506.53 To 263.53 291.74 T @ 200 p 1599.6351569.878 T @ 35 kP 1190.434 1178.954 T @ 250 kP 1093.652 1086.427 T(200P) − T(35 kP) 409.2009 390.9249 Resistivity A −2.6974 −3.1433 B 7362.617835.22 To −175.21 −98.68 R @ 200 p 28.24312 35.68633 Liquidus air 1040990 980 1030 1070 internal 1030 980 970 1015 1065 Pt 1005 965 960 10001050 phase Albite Orthoclase Orthoclase Cordierite Cordierite Liquidusviscosity 1794130.5 421516.23 Int liq - soft 145 66 59 99 140 estimated520319.01 39473174.9 73132031.9 4244242 631087.4 liquidus viscosityGlass 15 16 17 18 19 Weight Percent SiO₂ 58.52 58.87 58.17 58.33 58.51Al₂O₃ 17.87 17.98 17.76 17.81 17.87 B₂O₃ 9.85 9.91 9.79 9.82 9.84 MgO4.33 4.61 4.04 4.05 4.06 CaO 5.50 5.90 5.11 5.54 5.99 SrO 0 0 0 0 0 BaO0 0 0 0 0 Na₂O 0 0 0 0 0 K₂O 3.82 2.62 5.01 4.33 3.62 SnO₂ 0.12 0.120.12 0.12 0.12 Fe₂O₃ 0 0 0 0 0 total 100.01 100.01 100 100 100.01 MolePercent SiO₂ 63.35 63.35 63.35 63.35 63.35 Al₂O₃ 11.40 11.40 11.40 11.4011.40 B₂O₃ 9.20 9.20 9.20 9.20 9.20 MgO 6.98 7.40 6.56 6.55 6.55 CaO6.38 6.80 5.96 6.45 6.95 SrO 0 0 0 0 0 BaO 0 0 0 0 0 Na₂O 0 0 0 0 0 K₂O2.64 1.80 3.48 3.00 2.50 SnO₂ 0.05 0.05 0.05 0.05 0.05 Fe₂O₃ 0 0 0 0 0total 100 100 100 100 100 Properties strain 631 639 630 630 635 anneal683 689 683 682 687 softening point 914 913 921 918 922 CTE 41.5 39.643.3 41.6 40.4 density 2.412 2.43 2.4 2.404 2.408 Viscosity A B To T @200 p T @ 35 kP T @ 250 kP T(200 P) − T(35 kP) Resistivity A B To R @200 p Liquidus air 1110 1135 1085 1070 1075 internal 1100 1125 1070 10651060 Pt 1080 1105 1060 1050 1045 phase Cordierite Cordierite CordieriteCordierite Cordierite Liquidus viscosity Int liq - soft 186 212 149 147138 estimated 132273.398 64408.987 447990.94 482556.71 683059.804liquidus viscosity

TABLE 5 Glass 20 21 22 23 24 Weight Percent SiO₂ 57.49 57.65 57.82 58.4757.78 Al₂O₃ 17.55 17.6 17.65 17.86 17.64 B₂O₃ 10.85 10.88 10.91 9.8410.9 MgO 4 4 4.02 4.06 4.02 CaO 5.04 5.48 5.92 5.99 5.92 SrO 0 0 0 0 0BaO 0 0 0 0 0 Na₂O 0 0 0 0 0 K₂O 4.95 4.28 3.57 3.62 3.57 SnO₂ 0.12 0.120.12 0.16 0.16 Fe₂O₃ 0 0 0 0 0 total 100 100.01 100.01 100 99.99 MolePercent SiO₂ 62.65 62.65 62.65 63.33 62.63 Al₂O₃ 11.27 11.27 11.27 11.4011.27 B₂O₃ 10.20 10.20 10.20 9.20 10.20 MgO 6.50 6.48 6.49 6.55 6.49 CaO5.89 6.38 6.87 6.95 6.87 SrO 0 0 0 0 0 BaO 0 0 0 0 0 Na₂O 0 0 0 0 0 K₂O3.44 2.97 2.47 2.50 2.47 SnO₂ 0.05 0.05 0.05 0.07 0.07 Fe₂O₃ 100 100 100100 100 total Properties strain 623 630 632 637 630 anneal 673 680 682688 680 softening point 916 913 914 922 918 CTE 43.7 42.2 40.3 41.1 41density 2.394 2.395 2.401 2.411 2.405 Viscosity A −2.826 −2.7517 B6611.93 6318.79 To 284.22 304.73 T @ 200 p 1573.842 1555.299 T @ 35 kP1181.353 1170.820 T @ 250 kP 1088.206 1080.076 T(200 P) − T(35 kP)392.489 384.480 Resistivity A −4.9927 −2.6521 B 13663.94 5980.3 To−556.65 129.56 R @ 200 p 26.35204 34.86784 Liquidus air 1040 1050 10651060 1040 internal 1035 1045 1050 1055 1030 Pt 1020 1025 1030 1040 1020phase Cordierite Cordierite Cordierite Cordierite Cordierite Liquidusviscosity 565239.4 913330.2 Int liq - soft 119 132 136 133 112 estimated1542714 872242.2 740167 836776.9 2153251 liquidus viscosity Glass 25 2627 28 Weight Percent SiO₂ 58.61 57.36 56.92 58.14 Al₂O₃ 17.27 17.5117.39 17.03 B₂O₃ 9.86 10.82 10.74 10.45 MgO 4 3.98 3.96 3.85 CaO 6.36.61 7.31 5.67 SrO 0 0 0 0 BaO 0 0 0 0 Na₂O 0 0 0 0 K₂O 3.84 3.55 3.524.69 SnO₂ 0.12 0.16 0.16 0.16 Fe₂O₃ 0 0 0 0 total 100 99.99 100 99.99Mole Percent SiO₂ 63.35 62.10 61.55 63.15 Al₂O₃ 11.00 11.17 11.08 10.90B₂O₃ 9.20 10.11 10.02 9.8 MgO 6.45 6.43 6.38 6.23 CaO 7.30 7.67 8.476.60 SrO 0 0 0 0 BaO 0 0 0 0 Na₂O 0 0 0 0 K₂O 2.65 2.45 2.43 3.25 SnO₂0.05 0.07 0.07 0.07 Fe₂O₃ 100 100 100 100 total Properties strain 633628 630 624 anneal 683 677 677 674 softening point 918 907 901 911 CTE41.9 42 43.2 44.1 density 2.412 2.414 2.424 2.404 Viscosity A −2.6477−3.0308 −2.8977 −3.0702 B 6160.22 6642.81 6307 6906.16 To 314.38 271.68291.74 253.21 T @ 200 p 1559.188 1517.558 1504.921 1538.979 T @ 35 kP1170.945 1148.634 1139.254 1160.212 T @ 250 kP 1080.039 1059.7941052.019 1068.756 T(200 P) − T(35 kP) 388.243 368.924 365.667 378.766Resistivity A −2.6628 −2.9715 −2.7071 −3.4632 B 6172.99 6668.56 5845.088147.16 To 100.8 50.95 149.34 −101.76 R @ 200 p 37.14907 37.6207240.24979 31.79388 Liquidus air 1065 1060 1025 1010 internal 1050 10501015 1000 Pt 1040 1030 1000 990 phase Anorthite Anorthite AnorthiteAnorthite Liquidus viscosity 532706.2 319158 664567.2 1505199 Int liq -soft 132 143 114 89 estimated 872242.2 561623.8 1953516 7623399 liquidusviscosity

TABLE 6 Glass 29 30 31 32 33 34 35 36 37 38 Weight SiO₂ 56.19 56.3356.46 56.6 56.72 56.48 57.32 58.17 57.29 56.92 Percent Al₂O₃ 17.45 17.0116.56 16.11 15.66 17.77 17.52 17.27 17.03 16.63 B₂O₃ 11.27 10.63 9.989.33 8.68 11.17 9.70 8.21 9.26 9.38 MgO 2.78 2.61 2.43 2.26 2.08 2.762.39 2.01 2.27 2.29 CaO 4.62 4.36 4.10 3.84 3.58 4.57 3.94 3.31 3.773.84 SrO 5.83 5.52 5.20 4.89 4.57 5.76 5.00 4.23 4.79 4.88 BaO 0 0 0 0 00 0 0 0 0 Na₂O 1.68 3.37 5.06 6.77 8.48 1.30 3.92 6.56 5.39 5.86 K₂O 0 00 0 0 0 0 0 0 0 SnO₂ 0.18 0.18 0.21 0.21 0.23 0.18 0.20 0.23 0.21 0.21Fe₂O₃ 0 0 0 0 0 0 0 0 0 0 total 100 100.01 100 100.01 100 99.99 99.9999.99 100.01 100.01 Mole SiO₂ 62.18 62.16 62.14 62.12 62.10 62.56 63.2864.00 63.08 62.60 Percent Al₂O₃ 11.38 11.06 10.74 10.42 10.10 11.6011.40 11.20 11.05 10.78 B₂O₃ 10.76 10.12 9.48 8.84 8.20 10.68 9.24 7.808.80 8.90 MgO 4.58 4.29 3.99 3.70 3.40 4.56 3.93 3.30 3.72 3.75 CaO 5.485.16 4.84 4.52 4.20 5.42 4.66 3.90 4.45 4.52 SrO 3.74 3.53 3.32 3.112.90 3.70 3.20 2.70 3.06 3.11 BaO 0 0 0 0 0 0 0 0 0 0 Na₂O 1.80 3.605.40 7.20 9.00 1.40 4.20 7.00 5.75 6.25 K₂O 0 0 0 0 0 0 0 0 0 0 SnO₂0.08 0.08 0.09 0.09 0.10 0.08 0.09 0.10 0.09 0.09 Fe₂O₃ 0 0 0 0 0 0 0 00 0 total 100 100 100 100 100 100 100 100 100 100 Proper- strain 611 590578 565 620 589 577 577 576 ties anneal 659 636 622 607 670 635 623 625621 softening 887.1 856.5 831.1 807.2 780 899.5 866.3 850.5 843 836.1point CTE 41.6 47.7 53.9 59.6 40.4 48.1 56.6 52.8 55.4 density 2.4782.48 2.492 2.494 2.501 2.472 2.467 2.463 2.472 2.478 Viscos- A −2.475−2.209 −2.175 −2.086 −1.813 −2.817 −2.501 −1.845 ity B 5764.2 5523.25563.1 5506.2 4988.5 6843.6 6402.1 5180.5 To 306 290.2 258.9 231 242.7193.3 197.4 272  200 1512.9 1514.85 1501.76 1486.11 1455.26 1530.461530.61 1521.51  3000 1274.43 1261.55 1243.15 1220.77 1185.68 1280.61268.32 1245.39 30000 1135.13 1116.27 1095.19 1069.96 1035.77 1131.541114.85 1091.42 50000 1109.49 1089.74 1068.2 1042.53 1008.75 1103.841086.58 1063.64 Liquidus internal 1010 1025 1040 1020 980 1030 1020 10701010 1040 Liquidus 516159.7 203050.1 88539.17 78110.11 89722.76 238527.379513.84 viscosity Int liq - 122.9 168.5 208.9 212.8 200 130.5 153.7219.5 167 203.9 soft

TABLE 7 Glass 39 40 41 42 43 44 45 46 47 Weight SiO₂ 56.76 57.00 57.3357.72 58.11 59.01 56.88 57.06 57.30 Percent Al₂O₃ 17.19 16.95 17.5217.64 17.76 15.66 17.09 16.32 17.52 B₂O₃ 10.19 9.6 9.66 9.72 9.79 9.8410.20 10.72 9.70 MgO 2.50 2.35 2.37 2.81 3.26 2.45 2.56 2.65 2.39 CaO4.17 3.92 3.97 4.00 4.03 4.01 4.15 4.36 3.94 SrO 5.24 4.98 5.00 3.932.85 5.04 5.16 5.42 5.00 BaO 0 0 0 0 0 0 0 0 0 Na₂O 3.74 4.99 3.92 3.953.98 3.77 3.74 0 3.92 K₂O 0 0 0 0 0 0 0 3.24 0 SnO₂ 0.20 0.20 0.23 0.230.23 0.23 0.23 0.23 0.23 Fe₂O₃ 0 0 0 0 0 0 0 0 0 total 99.99 99.99 100100 100.01 100.01 100.01 100 100 Mole SiO₂ 62.63 62.78 63.3 63.3 63.3064.6 62.7 63.50 63.28 Percent Al₂O₃ 11.18 11.00 11.40 11.40 11.40 10.1011.10 10.70 11.40 B₂O₃ 9.70 9.13 9.20 9.20 9.20 9.30 9.70 10.30 9.24 MgO4.12 3.86 3.90 4.60 5.30 4.00 4.20 4.40 3.93 CaO 4.93 4.63 4.70 4.704.70 4.70 4.90 5.20 4.66 SrO 3.35 3.18 3.20 2.50 1.80 3.20 3.30 3.503.20 BaO 0 0 0 0 0 0 0 0 0 Na₂O 4.00 5.33 4.20 4.20 4.20 4.00 4.00 0.004.20 K₂O 0 0 0 0 0 0 0 2.3 0 SnO₂ 0.09 0.09 0.10 0.10 0.10 0.10 0.100.10 0.10 Fe₂O₃ 0 0 0 0 0 0 0 0 0 total Properties strain 589 578 596597 596 590 593 619 597 anneal 638 626 643 644 645 637 640 669 645softening point 858.5 843.2 867.6 867 876.9 859.5 858.5 898 873 CTE 48.451.7 48.1 47.3 46.1 47.6 48 44.2 47.2 density 2.477 2.474 2.475 2.4662.451 2.472 2.476 2.465 2.466 Viscosity A −2.549 −2.625 −2.625 −2.567 B6218.5 6434.5 6434.5 6097.1 To 233.8 223.8 223.8 303.3  200 1515.961530.02 1530.02 1555.78  3000 1265.72 1278.27 1278.27 1312.07 300001118.85 1129.8 1129.8 1168.86 50000 1091.76 1102.35 1102.35 1142.43Liquidus internal 1045 1040 1095 1080 1060 1015 1060 1050 1065 Liquidus130859 181336.2 321798.1 396638.1 viscosity Int liq - soft 186.5 196.8227.4 213 183.1 155.5 201.5 152 192

TABLE 8 Glass 48 49 50 51 Mole Percent SiO₂ 63 62.95 62.9 62.85 Al₂O₃ 1110.3 9.65 9 B₂O₃ 10.2 11.6 13.05 14.5 MgO 5.5 4.13 2.75 1.38 CaO 6.1 4.63.05 1.53 SrO 1.8 1.43 1.05 1.68 BaO 0 3.1 6.15 9.22 K₂O 2.4 1.8 1.2 0.6SnO₂ 0.1 0.1 0.1 0.1 Weight SiO₂ 57.2 54.9 52.9 51 Percent Al₂O₃ 16.915.3 13.8 12.4 B₂O₃ 10.7 11.7 12.7 13.6 MgO 3.34 2.42 1.55 0.75 CaO 5.173.74 2.4 1.16 SrO 2.81 2.16 1.53 0.95 BaO 0 6.91 13.2 19.1 K₂O 3.41 2.471.58 0.76 SnO₂ 0.23 0.22 0.21 0.2 Properties strain 628 609 603 598anneal 678 659 651 644 softening 909 890 876 858 CTE 42.8 43.9 45.4 46Density 2.44 2.516 2.606 2.677 Viscosity 200 1529 1525 1528 Internal1020 940 980 980 Liquidus Liquidus 822,000 5,233,000 1,100,000 Viscosity

TABLE 9 Example Mol % 52 53 54 55 56 57 58 59 MgO 2.1 2.1 2 2 2.2 2.351.9 CaO 21.2 20.6 20.1 19.85 21.65 13.2 25.6 20.8 SrO 8.7 BaO 2.1 2.1 22 2.2 2.35 1.9 RO 25.4 24.8 24.1 23.85 26.05 21.9 30.3 24.6 B₂O₃ 2.5 57.5 8 Al₂O₃ 8.8 8.6 8.4 8.25 6.05 10.1 11.7 9.4 SiO₂ 63.2 61.5 59.9 67.867.8 59.9 57.9 65.9 SnO₂ 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 T_(str) 676~660 643 711 699 648 710 715 α 52.8 ~52.5 52.2 50.4 54.6 50.4 57.5 50.3ρ 2.674 ~2.66 2.64 2.652 2.675 2.696 2.771 2.664 T_(liq) 1120 1150 11351190 η_(liq) (kP) 5.4 T₂₀₀ 1360

TABLE 10 Example Mol % 59 60 61 62 63 64 65 66 MgO 5 5 10 2.9 8.7 5.28.5 CaO 24 21 18 21 32.1 8.7 10.45 8.5 SrO 16 14 12 14 5.2 BaO 2.9 8.655.2 8.4 ZnO 5 RO 45 40 40 40 37.9 26.05 26.05 25.4 B₂O₃ 15 15 15 15 2.5Al₂O₃ 20 20 20 20 14.6 9.05 9.05 8.8 SiO₂ 20 25 25 25 47.4 64.8 64.863.2 SnO₂ 0.1 0.1 0.1 0.1 T_(str) 619 620 621 606 ~700 704 703 ~680 α73.7 70 67.3 69.9 ~66 52.4 53.5 ~52 ρ 2.885 2.865 2.853 ~2.84 T_(liq)1130 η_(liq) (kP) T₂₀₀

TABLE 11 Example Mol % 67 68 69 70 71 72 73 74 MgO 8.3 8.05 5.1 4.95 4.82.7 2.6 4.1 CaO 8.3 8.05 10.15 9.9 9.6 2.9 2.0 9.9 SrO 5.1 4.95 4.8 11.89.6 3.3 BaO 8.2 8 5.1 4.95 4.8 0.7 3.6 2.2 ZnO RO 24.7 24.1 25.4 24.724.1 18.0 17.7 19.4 B₂O₃ 5 7.5 2.5 5 7.5 9.0 7.5 9.7 Al₂O₃ 8.6 8.4 8.88.6 8.4 9.6 9.3 10.0 SiO₂ 61.6 59.9 63.2 61.6 59.9 63.3 65.4 60.8 SnO₂0.1 0.1 0.1 0.1 0.1 0.10 0.10 0.10 T_(str) ~655 633 ~680 ~660 639 645649 639 α ~51.5 51 ~53 ~53 53.1 46.2 46.5 46.5 ρ ~2.82 2.803 ~2.82 ~2.802.766 2.70 2.75 2.70 T_(liq) 1125 1080 1135 1080 1140 1130 1110 1045η_(liq) (kP) 25.1 40.2 T₂₀₀ 1383 1420

TABLE 12 Example Mol % 75 76 77 78 79 80 81 82 MgO 1.8 0 2.0 1.98 1.972.5 3.5 4.5 CaO 11.0 10.0 9.0 1.3 0.8 7.0 5.5 4.5 SrO 2.9 9.0 8.0 11.911.5 1.5 2.0 2.0 BaO 3.3 0 0 2.0 4.0 7.0 7.0 7.0 ZnO RO 19.0 19.0 19.017.2 18.3 18.0 18.0 18.0 B₂O₃ 10.7 8.0 8.0 6.4 6.4 9.0 9.0 9.0 Al₂O₃ 8.59.0 9.0 8.7 8.6 9.0 9.0 9.0 SiO₂ 62.3 64.0 64.0 67.6 66.5 63.9 63.9 63.9SnO₂ 0.07 0.10 0.10 0.17 0.17 0.10 0.10 0.10 T_(str) 631 648 649 667 665632 632 635 α 46.0 48.4 45.8 45.9 46.6 46.5 45.9 45.8 ρ 2.67 2.63 2.722.77 2.73 2.72 2.72 T_(liq) 1075 1150 1145 1100 1075 1050 1025 1020η_(liq) (kP) 124 235 166 364 437 T₂₀₀ 1563 1545 1490 1490 1494

TABLE 13 Example Mol % 83 84 85 86 87 88 89 MgO 3.8 3.9 1.8 0.0 2.0 2.02.0 CaO 6.0 5.7 11.0 10.0 9.0 1.3 0.8 SrO 2.2 2.5 2.9 9.0 8.0 11.9 11.5BaO 7.6 6.2 3.3 0 0 2.0 4.0 ZnO RO 19.5 18.3 19.0 19.0 19.0 17.2 18.3B₂O₃ 9.8 9.8 10.7 8.0 8.0 6.4 6.4 Al₂O₃ 9.8 9.9 8.5 9.0 9.0 8.6 8.6 SiO₂60.9 62.0 62.3 64.0 64.0 67.6 66.5 SnO₂ 0.10 0.10 0.07 0.10 0.10 0.170.17 T_(str) 630 631 613 648 649 667 665 α 48.2 46.0 46 48.4 45.8 45.946.6 ρ 2.77 2.71 2.67 2.63 2.72 2.77 T_(liq) 1045 1075 1150 1145 11001075 η_(liq) (kP) 106 124 235 T₂₀₀ 1443 1563 1545

Example 2

An experiment was performed to empirically demonstrate the impact ofresidual stress on CdTe device performance using glass substrates withvarying CTE. The experiment consisted of fabricating CdTe devices usingthe vapor transport deposition process on three different glasssubstrates having a CTE of 3.1, 4.3 and 8.5 ppm/° C., respectively. FIG.3 summarizes the residual stress and the corresponding efficiencies forthe CdTe devices fabricated on each of the three glass substrates. Theefficiencies were calculated using the following equation:Eff=V _(OC) ×J _(SC) ×FFwhere the open circuit voltage VOC, the short circuit JSC and the fillfactor FF are the device parameters that were extracted from thecurrent-voltage behavior of each solar cell devices under AM1.5irradiance at 25° C. The residual stress profile in the CdTe film wasmeasured by glancing incidence x-ray diffraction over a range of (hkl)and at different incident beam angles. Uniform stress (σ) from a givendirection (Ψ) results in uniform lattice strain (εΨ), which causesangular peak displacement, while non-uniform stress distorts peak shape.The measured strain is related to the applied stress by the elasticcompliance coefficients. The in-plane strain-stress relationship forf.c.c. materials is:

$ɛ_{\Psi}^{hkl} = {\left( \frac{d_{\Psi} - d_{0}}{d_{0}} \right)^{hkl} = {\sigma\left\lbrack {\frac{\left( {{2S_{11}} + {4S_{12}} - S_{44}} \right)}{3} + {\left( \frac{S_{44}}{2} \right)\sin^{2}\Psi}} \right\rbrack}}$The CdTe compliance coefficients are S₁₁=4.25×10−11 Pa, S₁₂=−1.73×10−11Pa, and S₄₄=5.02×10−11 Pa. The measured (hkl) peak positions werereduced to the substrate reference frame and the residual stressassociated with each peak was calculated.

To explain the results, we first we note that the CTE of the CdTe filmcan range from ˜5.5 to ˜6.5 ppm/° C. and is largely influenced by theCdTe deposition process which was noted earlier in this case to be byvapor transport. By convention, negative stress indicates in-planecompression (tension normal to substrate) and positive stress indicatesin-plane tension (compression normal to substrate). The CdTe filmdeposited on the 8.5 ppm/° C. CTE glass is relatively relaxed at thesurface and under significant in-plane compression within the film. TheCdTe film deposited on the 4.3 ppm/° C. CTE substrate is under in-planetension at the exposed surface and become more relaxed within the bulk,but with slight in-plane tension. The CdTe film deposited on the 3.1ppm/° C. CTE substrate exhibit mixed stress at the surface and is underin-plane tension in the bulk. The mean residual bulk stress for this setof samples exhibits a linear correlation with glass CTE. The interceptCTE for which no strain is expected in this case is ˜6 ppm/° C. Thecorresponding efficiency indicates a trend of increased efficiency asthe residual stress magnitude decreases as illustrated by the greydashed trace. This suggests a CdTe device with no residual stress in thefilm will exhibit optimum solar cell conversion efficiency.

To further illustrate the impact of the substrate CTE on CdTe solar celldevice performance, another experiment was performed to empiricallydemonstrate the impact of residual stress on CdTe device performanceusing glass substrates with varying CTE. In this case, the experimentconsisted of fabricating CdTe devices using the close spaced sublimationdeposition process on glass substrates with CTE of 4.1, 5.8, 6.6 and 8.6ppm/° C., respectively. Unlike the earlier described experiment, theglass substrates in this experiment were from the same alkali-freecomposition family so as to limit/mitigate any non-intended variablesthat could influence the experiment outcome. FIG. 5 summarizes theresidual stress and the corresponding efficiencies for the CdTe devicesfabricated on each of the glass substrates. As in FIG. 3, here we alsoobserve the mean residual bulk stress for this set of samples exhibits alinear correlation with glass CTE. In this case, the intercept CTE forwhich no strain is expected is ˜5.5 ppm/° C. And again, thecorresponding efficiency indicates a trend of increased efficiency asthe residual stress magnitude decreases as illustrated by the dashedtrace.

Stress and strain are known to cause microstructural defects insemiconductor films that can degrade the electrical performance ofdevices made thereafter in the film. In the case of CdTe solar cells, itis suggested that the defect density in the CdTe film follows a directtrend with the residual stress magnitude in the film: higher residualstress leads to higher defect density. Higher defect density then leadsto higher recombination losses in the bulk of the film which then leadsto lower open circuit V_(OC). Lower V_(OC) then leads to a lowerefficiency. To this point, the devices summarized in FIG. 4 receivedadditional characterization to demonstrate the impact of CdTe filmdefect density on the corresponding solar cell efficiency. The carrierconcentration was calculated from the capacitance-voltage measurementthat was performed on each solar cell device. The carrier concentrationprofile was then mapped into a device model that was constructed withinthe framework of a 2-D physics-based semiconductor device model fromSILVACO TCAD software. The defect density was then extracted by fittingthe measured current density-voltage curves. FIG. 5 shows the efficiencyand the corresponding extracted defect density as a function of the CdTefilm residual stress for the same devices in FIG. 4. Using the dashedlines as a guide, it can be shown that the defect density approachesminimum and the efficiency approaches optimum where the magnitude of theresidual stress in the CdTe film is minimal.

The alkalis in the glass and low melting temperature combine toaccelerate melting thus enabling high volume, low-cost melting andforming relative to alkali-free alternatives while retaining competitiveproperties, including in particular mechanical and dimensional stabilitywhen reheated to high temperature. These glasses are well suited forlarge-volume sheet glass applications, particularly OLED lighting andcadmium telluride (CdTe) photovoltaics, for which thermal stability,large volumes, and low cost are desirable substrate attributes.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A glass comprising about, in mol %: 60-65 SiO₂5-15 Al₂O₃ 4-11 B₂O₃ 0-5 MgO less than 7 CaO 0-12 SrO 0-8 BaO and 9-35RO, wherein the glass comprises no purposefully added M₂O, and wherein Mis an alkali metal and wherein R is an alkaline earth metal.
 2. Theglass of claim 1, comprising about 61-64 mol % SiO₂.
 3. The glass ofclaim 1, comprising about 8-11 mol % Al₂O₃.
 4. The glass of claim 1,comprising zero mole percent M₂O.
 5. The glass of claim 1, furthercomprising less than 2 mol % of TiO₂, MnO, ZnO, Nb₂O₅, MoO₃, Ta₂O₅, WO₃,ZrO₂, Y₂O₃, La₂O₃, HfO₂, CdO, SnO₂, Fe₂O₃, CeO₂, As₂O₃, Sb₂O₃, Cl, Br,P₂O₅, or combinations thereof.
 6. The glass of claim 1, wherein theglass satisfies the ratio:0.4≤(CaO (mol %))/(CaO (mol %)+SrO (mol %))≤1.0.
 7. The glass of claim1, wherein the glass has a coefficient of thermal expansion of fromabout 4.0 to about 7.5 ppm/° C. from 25 to 300° C.
 8. The glass of claim7, wherein the glass has a coefficient of thermal expansion of fromabout 4.0 to about 6.5 ppm/° C. from 25 to 300° C.
 9. The glass of claim8, wherein the glass has a coefficient of thermal expansion of fromabout 4.0 to about 6.0 ppm/° C. from 25 to 300° C.
 10. The glass ofclaim 1, wherein the glass is in the form of a glass sheet having athickness of 2.0 mm or less.
 11. The glass of claim 10, furthercomprising a transparent conductive oxide on at least one side of theglass sheet.
 12. The glass of claim 10, wherein the glass is thermallytempered.
 13. An article comprising the glass of claim
 1. 14. Thearticle of claim 13, wherein the article comprises an electronic device.15. The electronic device of claim 14, wherein the device comprises aphotovoltaic, photochromic, electrochomic, or organic light emittingdiode device.